Safety control system



SAFETY CONTROL SYSTEM Filed March 28, 1935 Patented Apr. 18, 1939 UNITED STATES PATENT OFFICE SAFETY CONTROL SYSTEM Application March 28, 1935, Serial No. 13,486 v 13 Claims. (Cl. 158-28) 10 usually operated according to the amount of draft in the stack so that upon an increase in stack draft the draft stabilizer is moved to one position to restrict the amount of draft through the boiler and upon a decrease in stack draft the draft stabilizer is moved to another position to increase the draft through the boiler. By using draft stabilizers, the combustion in the boiler may be quite accurately controlled to give a greater efficiency in boiler operation.

Also, in combustion devices such as boilers, it is usual to provide a stand-bydamper between the boiler and the stack to prevent heat losses from the boiler during stand-by periods. When the combustion device is placed in operation this stand-by damper is opened either mechanically orby the draft to allow escapement of the gases of combustion into the stack. When the combustion device is placed out of operation during stand-by periods, this stand-by damper is moved to a closed position to prevent the escapement of the hot gases from the combustion device. In this manner, heat losses in the combustion de-. vice are greatly minimized.

However, frequently these draft stabilizers or stand-by dampers become stuck in the closed or draft restricting position which closes off the draft through the boiler. Upon the sticking of the draft stabilizer or stand-by damper in this draft preventing position, there is no escape for the combustible gases from the boiler. The accumulation .of large amounts of combustible gases in the boiler becomes exceedinglydangerous in that if they are sufficiently ignited serious explosions may occur or they may escape from the boiler into the surrounding atmosphere and contaminate the same. v

Therefore, as a safety feature, somemeans must be provided to.prevent operation of the firing means of the boiler in case the draft stabilizer or stand-by damper becomes stuck in the closed or draft restricting position.

Consequently, it is an object of this invention to provide a safety control for a boiler utilizing a draft stabilizer or a stand-by damper to prevent 55 firing of the boiler in case the draft stabilizer should become stuck in closed or draft restricting position.

Another object of this invention is to provide a safety control for a boiler utilizing a draft stabilizer or a stand-by damper and a time controlled safety device which prevents operation of the firing means in case combustion is not established upon starting wherein a draft stabilizer or a stand-by damper safety device coacts with the time control safety device to prevent operation of the firing means in case the draft stabilizer or stand-by damper becomes stuck in a closed or draft restricting position.

A further object is to provide a safety control for a boiler utilizing a draft stabilizer or a standby damperand' a time controlled safety device which prevents operation of the firing means in case combustion is not established at starting wherein a draft stabilizer or a stand-by damper safety device coacts with the time control safety device to prevent operation of the firing means in case the draft stabilizer or stand-by damper becomes stuck in closed position but which will not prevent operation of the firing means if the draft stabilizer or stand-by damper is only momentarily moved to closed position.

A still further object is to providea switching mechanism operated by a draft stabilizer or a stand-by damper to control the operation of the firing means of .a boiler.

Other objects and advantages will become apparent to those skilled in the art upon reference to the accompanying specification, claims, and drawing in which:

Fig. 1 is a diagrammatic illustration of a boiler with one form of my invention associated therewith;

Fig. 2 is a perspective view of a conventional draft stabilizer with the switch of my invention attached thereto for operation thereby;

Fig. 3 is a perspective view of a conventional stand-by damper for preventing heat losses through the stack during stand-by periods with the switch of my invention attached thereto for operation thereby; and

Fig. 4 is a diagrammatic View of a portion of the system disclosed in Fig. 1 showing the standby damper safety control applied thereto.

Although my invention may be applied to any type of heating system or power system, it is shown to be applied to a boiler heating system wherein a steam or hot water boiler is designated at I0. Steam or hot water is led from the boiler l0 by means of a pipe H for use atv some remote point, and I2 designates a return pipe delivering the used fluid back to the boiler I8. The steam or water is heated in the boiler III preferably by means of an electrically operated oil burner I3, having a nozzle I 4 extending into the combustion chamber of the boiler I8. Ex-

pended gases of combustion are exhausted from the boiler I8 by means of a flue or bridge I5 extending into a conventional stack I6. The gases are drawn from the combustion chamber or boiler I8 by means of the draft existing in the stack I6.

In order to regulate the rate at which the expended gases are taken from the boiler I8 and consequently the draft in the boiler I8, a draft regulator generally designated at I! is provided in the flue or bridge I5. By referring to Fig. 2, it will be seen that the draft regulator or draft stabilizer I'I comprises a damper I8 movable in the flue I5. The damper I8 is secured to a shaft I9 for rotation therewith. The shaft I9 extends outwardly through the flue I5 and has secured on the end thereof an arm 28. A weight 2I is secured to the arm 28 in an adjustable manner to provide a biasing means for urging the damper I8 towards open position. The other end of shaft I9 which also extends through the flue I5 carries a clamp 22 for rotation therewith. The clamp 22 carries preferably a mercury switch 23 of usual design.

The damper I8 is normally maintained in an open position by means of the biasing weight 2I but upon an increase in draft in the stack I6, the damper I8 will be drawn towards a closed position against the bias of the weight 2|. In this manner, the amount of draft passing through the boiler I8 may be maintained substantially constant. The mercury switch 23 is so positioned with respect to the damper I8 that when the damper I8 is in a vertical or closed position, the mercuryswitch 23 is in open circuit position and that when the damper moves out of this closed position the mercury switch is tilted to circuit closed position.

In order to prevent heat losses through the stack I6 during stand-by periods, a stand-by damper generally designated at H is provided in the flue I5 (Fig. 4). By referring to Fig. 3,

one type of stand-by damper is shown wherein, it will be seen that the stand-by damper I'I' comprises a damper I 8' movable in the flue I5. The damper I8 is secured to a shaft I9 for rotation therewith. The shaft I9 extends outwardly through the flue I5 and has secured at the end thereof an arm 28'. A weight 2I' is secured to the arm 28 in an adjustable manner to provide a biasing means for urging the damper I 8' towards a closed position. The other end of the shaft I9 extends through the flue I5 and carries 'a clamp 22 for rotation therewith. The clamp 22' carries preferably a mercury switch 28' of usual design.

The damper I8 is normally maintained in a closedor draft restricting position by means of the biasing weight H, but upon the starting up of the electrically operated oil burner I3, gases will be caused to flow through the flue I5 and the damper I8 will be pushed towards an open position against the bias of the weight 2|. In-

this manner, the flue is closed during stand-by periods when the oil burner I3 is not operating and is opened when the oil burner I3 is operating. Although I have shown a stand-by damper that is controlled by the flow of gases thereby, it is within the contemplation of this invention to use a mechanically operated damper to ac- ,complish the same results.

The mercury switch and 26 leading from some source not shown.

Connected to line wire 25 is a wire 21 which leads to a stationary contact 28. Cooperating with the contact 28 is a switch arm 29 which is connected by means of wires 38 and 3I to a terminal box 32 of the electrically operated oil burner I3. The terminal box 32 is connected by means of wires 33 and 34 to the other line wire 26. Connected to wires 38 and 33 are wires 35 and 36 respectively which connect to opposite ends of a primary 3! of a step up transformer 38. The secondary 39 of the step up transformer 38 is connected by means of wires 48 and M, respectively, to ignition electrodes 42 and 43.

From the above, it is seen that upon closing switch 29 circuits are completed to the terminal box 32 and ignition electrodes 42 and 43 to operate the electrically operated oil burner I3 and to ignite oil delivered thereby to start and maintain combustion in the combustion space of the boiler I8. Combustion is stopped by opening the above circuits by moving switch arm 29 away from stationary contact 28.

A step down transformer is designated at 41, the primary 48 of which is connected by means of wires 45 and 48 to the line wires 25 and 26 respectively. The step down transformer 41 has a secondary 49.

A safety switch is designated generally at 58, preferably of the type shown and described in Patent No. 1,958,081 to Frederick S. Denison, patented May 8, 1934. The safety switch 58 comprises spring pressed contacts 5I and 52 that are normally urged apart and which are held latched into engagement with each other by means of the bimetal strips 53 and 54. 55 designates a heater resistance which, when energized, gives off heat to warp the bimetal strip 53 to the left out of engagement with the contact 5| to permit separation of contacts 5I and 52. The bimetal strip 54 which is not effected by the heating element 55 warps in an opposite direction with respect to the bimetal strip 53 to compensate for ambient temperature changes. When the bimetal 53 has been warped by the action of heating element 55 to release contact 5I, contact 5I can be made to engage contact 52 only by manual resetting of the switch in the manner pointed out in the Denison patent.

A condition responsive device is designated at 58 and is preferably in the form of a thermostat which is secured in place by means of a binding post 51. The thermostatic device carries contacts 58' and 58 which engage at predetermined temperature conditions with stationary contacts 58 and GI respectively. The distance between contacts 58 and 68 is less than the distance beengages contact 68 before contact 59 engages contact 6L.

A.relay coil is designated at 62 and by means of suitable connections the relay coil upon energization thereof will move a switch arm 63 into engagement with a contact 54 and the switch arm- 29 into engagement with the contact 28.

Upon deenergization of relay coil 62, the switch arms 63 and 29 will be moved out of engagement with contacts 64 and 28 respectively by some means such as gravity or springs not shown.

Located in the flue between the boiler l9 and the draft stabilizer I1 is a thermostatic stack switch 65 preferably of the type disclosed in Patent No. 1,946,598 to Daniel G. Taylor and patented February 13, 1934. The thermostatic stack switch 65 has a bimetal helix extending into the flue so that temperature changes will operate a slip friction device designated at 66. The slip friction device 66 moves a switch arm 61 between contacts 68 and 69. Upon a decrease in temperature in the flue l5, the bimetal and slip friction device 66 will move the switch arm 61 into engagement with the cold contact 68 and upon an increase in temperature in the flue 5, the bimetal and slip friction device 66 will move the switch arm 61 into engagement with the hot contact 69. a

One end of the secondary 49 of the step down transformer 41 is connected by means ,of a wire 19 to the contact 5| of the safety switch 59. The contact 52 of the safety switch 59 is connected by means of a wire 1| to the stationary contact 69 of the thermostat 56. The stationary contact 6| of the thermostat 56 is connected by means of a wire 12 to the cold contact 68 of the thermostatic stack switch 65. The switch arm 61 of the thermostatic stack switch 65 is connected by means of a wire 13 to a wire 14 which is in turn connected to one end of theheating ele ment 55 of the safety switch 59. The other end of the heating element 55 is connected by means of a wire 15 to one end of the relay coil 62. The other end of the relay coil v62 is connected by means of a wire 16 to the other end of secondary 49 of the step-down transformer 41.

Upon a decrease in temperature affecting the thermostat 56, contact 58 will engage contact 69 and upon a further decrease in temperature contact 59 will engage contact 6|. 4 When both contacts 58 and 59 engage stationary contacts 69 and 6|, a starting circuit is completed from the secondary 49 of the step-down transformer 41 through wire 19, contact 5|, contact 52, wire 1|,

contact 69, contact 58, contact 59, contact 6|, wire 12, cold contact 68, switch arm 61, wire 13, wire 14, heating element 55, .wire 15, relay coil 62, and wire 16 back to the secondary of trans- Upon completion of such circuit the heating. element 55 is energized and the relay 62 is energized to move switch arms 63 and 29 into engagement with contacts 64 and 28 to start operation of the oil burner |3. The bimetal 53 will not be immediately affected by the energizertion of the heating element 55, some time lag being necessary to warp the bimetal sufficiently 53 to open contacts 5| and 52.

Binding post 51 ofthermostat 56 is connected by means of a wire 11 to the contact 64 and the switch arm 63 is connected by means of a wire 16 to the wire 14. By means of wires 11 and 14 and by means of closing of switch 63 with contact 64 upon energization of the circuit above described, a second or holding circuit is completed from one end of the secondary .49 of step-down transformer 41 through wire-19, contacts 5| and 52, wire 1|, contacts 69 and 58, thermostat 56, binding post 51, wire 11, contact 64, switch arm 63, wire 18, wire 14, heating element 55, wire 15, relay coil 62 and wire 16 back to secondary 49 of transformer 41. By reason of this holding circuit, the cold contact 68 of the stack switch 65 is shunted out, relay coil 62 is maintained energized to maintain the switch arms 29 and 63 in engagement with the contacts 28 and 64 respectively to continue heating of the heating element 55 of the safety switch 59 and to continue operation of the electrically operated fuel burner I3.

The hot contact 69 of the thermostatic stack switch 65 is connected by means of a wire 89 to one of the electrodes of the mercury switch 23 or the mercury switch 23 operated by the draft stabilizer IT or by the stand-by damper l1. The other electrode of the mercury switch 23 or the mercury switch 23 is connected by means of a wire 8| to the connection of wire 15 and relay 62. (See Figs. 1 and 4.)

If the fuel supplied by the fuel burner I3 is properly ignited by the ignition means 42 and 43 and combustion has been established in the combustion chamber of the boiler Hi, the temperature of the combustion gases passing through the flue l5 will increase, which increase will move switch arm 61 out of engagement with the cold contact 68 and into engagement with the hot contact 69. Also, if the draft stabilizer H or the stand-up damper is opened and not in a draft restricting position, the electrodes of mercury switch 23 or mercury switch 23' will be engaged by the usual mercury contained therein,

{issuming now that-combustion has been established and has been properly reflected by the thermostatic stack switch 65 to move switch arm 61 into engagement with the contact 69, and that the draft stabilizer H or stand-by damper l1 is not stuck in a closed or draft restricting position so that'contact-between the two electrodes of mercury switch 23 or the mercury switch 23 is made by the mercury contained therein, a safety switch shorting circuit will be completed from secondary 49 of the step down transformer 41 through wire 19, contacts 5| and 52, wire 1|, contacts 69 and 58, thermostat 56, binding post 51, wire 11, contact 64, switch arm 63, wire 18, wire 13, switch arm 61, contact 69, wire 89, the electrodes and mercury of mercury switch 23 or of mercury switch 23', wire 8|, relay 523 and wire 16 back to the secondary 49 of step-down transformer 41. By reason of this safety switch shorting circuit, the heating element 55 of safety switch 59 is shunted out so that the bimetal 53 will not be warped to open contacts 5| and 52. This safety switch shorting circuit includes the relay coil 62 to maintain the same energized to maintain switch arms 29 and 63 in engagement with contacts 28 and 64 to maintain the oil burner |3 in operation.

Should the temperature in the flue l5 decrease by reason of a failure in combustion in the boiler l9 by accident or other reason, this decrease in temperature will operate the slip friction device 66 to move the switch arm 61 out of engagement with the hot contact 69 to break this safety switch shorting circuit which would then cause energization of heating element 55 to warp the bimetal 53 to break the contacts 5| and 52 to deenergize the relay coil 62 to stop operation of the fuel oil burner l3. Likewise, should the draft stabilizer H or the stand-by damper |1' become stuck in closed position or in a draft restricting position, contact between the electrodes of merdraft restricting or closed position for a period longer than required to warp sufiiciently the bimetal strip 53 upon heating of heating element 55, then contacts 5i and 52 will be separated to deenergize relay coil 52 to open switch arms 29 and 63 with respect to contacts 28 and 54 to stop operation of the oil burner i3. However, if the draft stabilizer II or stand-by damper II should be moved to closed position or draft restricting position only momentarily or for a time less than that required to completely warp bimetal 53 to break contacts 5| and 52 to cause shut down, there will be no shut down.

If, upon starting up of the oil burner in the manner above described, the draft stabilizer l'l or the stand-by damper II should be stuck in a closed or draft restrictingposition, operation of the oil burner I3 will after a time be prevented. With the draft stabilizer or stand-by damper in such a position, .the starting and holding circuits would be completed to start operation of the oil burner l3 but the safety switch shorting circuit could not be completed whereby heating element 55 would cause warping of the bimetal 53 to break contacts 5| and 52 to deenergize the relay 52 to open switch 29 with respect to contact 28 to stop operation of oil burner l3. Therefore, if the draft stabilizer H or the stand-by damper I1 is stuck in closed position at starting, the oil burner I3 is only run for a period of time that is required to warp bimetal 53 under the action of heating element 55.

From the above. it is seen that I have invented a safety control system for a boiler utilizing a draft stabilizer or a stand-by damper and a time control safety device which prevents operation of the firing means-in case combustion is not established at starting wherein a draft stabilizer or a stand-by damper safety device coacts with the time control safety device to prevent operation of the firing means in case the draft stabilizer or stand-by damper becomes stuck in closed position at starting and to stop operation after starting in case the draft stabilizer or stand-by damper becomes stuck in closed position but which will not prevent operation of the firing means if the draft stabilizer or stand-by damper is only momentarily moved to closed position by some brief condition affecting the fiow of gases through the Various modifications may be made in the system embodying my invention without departing from the spirit and scope thereof and I desire, therefore, that only such limitations shall be placed thereon as are imposed by the prior art or art set forth in the appended claims.

I claim as my invention:

1. In a system of the class described, a heater, firing means for the heater, a draft switch closed upon the occurrence of normal draft conditions in the heater, a combustion responsive switch closed upon the establishment of combustion, a safety switch including a heater, a control switch,

circuit connections between the control switch,

safety switch, safety switch heater and firing means to cause operation of the firing means and heating of the safety switch heater, and circuit connections between said control switch, safety switch, draft I switch, combustion responsive switch and firing means for shunting said safety switch heater to maintain the firing means in operation upon the establishment of combustion and during normal draft conditions.

2. In a system of the class described, a heater, firing means for the heater, a damper positioned for controlling the draft through the heater, and control meansfor controlling the operation of the firing means including means for preventing operation of the firing means upon failure of combustion or upon movement of the damper to a draft preventing position for a predetermined time interval but permitting operation of the firing means if the damper is moved only momentarily to draft preventing position.

3. In a system of the class described, a heater, firing means for the heater, a damper positioned for controlling the draft through the heater, a timing means operatively associated with the firing means and operative to stop operation-of thefiring means following operation of the timing means for a predetermined time interval, control means for said firing means and said timing means for placing said firing means and said timing means in operation, means responsive to the establishment of combustion for stopping operation of the timing means to continue operation of the firing means, and means to continue operation of the timing means to stop operation of the firing means when the-damper is maintained in ya draft preventing position.

4. In a system of the class described, a heater, firing means for the heater, a damper positioned for controlling the draft through the heater, a timing means operatively associated with the firing means and operative to stop operation of the firing means following-operation of the timing means for apredetermined time interval, control means for said firing means and said timing means for placing said firing means and said timing'means in operation, means responsive to the establishment of combustion for stopping operation of the timing means to continue operation of the firing means, and means to continue operation of the timing means to stop operation of the firing means when the damper is maintained in a draft preventing position for a predetermined time.

5. In a system of the class described, a heater, firing means for the heater, a damper positioned for controlling the draft through the heater, a timing means operatively associated with the firing means and operative to stop operation-of the firing means following operation of the timing means for a predetermined time interval, control means for said firing means and said timing means for placing said firing means and said timing means in operation, means responsive to the establishment of combustion for stopping operation of the timing means to continue operation .of the firing means, and means operated by said damper to continue operation of the tim- 1 ing means to stop operation of said firing means in case said damper is maintained in draft preventing position.

6. In a system of the class described, a heater, firing means for the heater, a damper positioned for controlling the draft through the heater, a timing means operatively associated withthe firing .means and operative to stop operation of the firing means following operation of the timing means for a predetermined time interval, control means for said firing means and said timing means for placing said firing means and said timing means in operation, means responsive to the establishment of combustion for stopping operation of the timing means to continue operation of the firing means, and means operated by said damper to continue operation of the timing] means to stop operation of said firing means in case said damper is maintained in draft preventing position for atleast a predetermined length of time and for preventing operation of the timing means to stop operation of said firing means in case said damper is not maintained in draft preventing position for said predetermined length of time.

7. In a system of the class described, a heater, firing means for said heater, a damper for said heater, a switch operated by said damper, a circuit controlled by said switch, means responsive to movement of said damper to closed position to operate said switch to open the circuit controlled thereby, and means responsive to the opening of said circuit to prevent operation of said firing means if said circuit remains opened a predetermined period of time but permitting operation of said'firing means if said circuit is only momentarily opened.

8. In a system of the class described comprising, a heater, firing means for the heater, time delay means for controlling the operation of the firing means, control means including said time delay means for preventing operation of the firing means upon a failure of combustion for a predetermined length of time, and control means including said time delay means for preventing operation of the firing means in response to the existence of a different condition within said heater for a predetermined length of time, making the operation of the firing means unsafe, but permitting operation of the firing means if such condition exists for a short time only.

9. In a system for controlling the supply of fuel to a furnace, a switch for preventing the supply of fuel to the furnace and having an element which is required to be energized for a predetermined time interval befoi'e said switch will operate to prevent the supply of fuel, a combustion responsive switch, a furnace draft condition responsive switch, and means responsive to operation of said last named switches for causing the energization of said element and operation of said first named switch to stop the supply of fuel upon failure of combustion or operation of said draft condition responsive switch due to the continued existence of an improper furnace condition.

10. In a system for controlling the supply of fuel to a furnace, a switch for preventing the supply of fuel to the furnace and having an element which is required to be energized for a predetermined time interval before said switch will operate to prevent the supply of fuel, a combustion responsiveswitch, a furnace condition responsive switch, and means responsive tooperation of said last named switches for causing the energization of said element and operation of said first named switch to stop the supply of fuel upon failure of combustion or operation of said condition responsive switch due to the'continued existence of an improper furnace condition.

11. The combination, comprising means to control the supply of fuel to a furnace, a time delay operating switch operative to stop said sup- 7, ply of fuel, a combustion responsive switch. a

furnacecondition responsive switch, and means for operating said time delay switch to stop said supply of fuel in response to either operation of said combustion responsive switch due to failure of combustion or operation of said condition responsive switch due to the existence of improper furnace conditions for a predetermined time interval.

12. A control system for a heater having firing means, comprising in combination, a combustion responsive switch closed upon the establishment of combustion, a switch operated in'response to a condition prevailing in the heater which, when abnormal, renders operation of the firing means undesirable, said switch opening upon the condition becoming abnormal, a safety switch including a heater, a control switch, circuit connections between the control switch, safety switch, safety switch heater and firing means to cause operation of the firing means and heating of the safety switch heater, and a shunt circuit for said safety switch heater including the condition responsive switch and the combustion responsive switch to prevent the opening of the safety switch as long as combustion is established and theheater conditionis normal but to permit opening of the safety switch to thereby shut down the firing means if the heater condition is abnormal for a; predetermined period of time.

13. In combination, electrical means to feed fuel to a furnace, a normally closed safety switch which when open deenergizes said fuel feeding means and must be manually reclosed, a thermal element which when heated to a predetermined extent opens said safety switch, an electrical heating element for said thermal element, a main control switch for energizing said fuel feeding means and heating element upon a demand for heat, a combustion responsive switch, a switch controlled by a condition of the furnace, and electrical connections between the heating element, combustion switch and furnace condition switch to deenergize said heating element while permitting continued energization of said fuel feeding means when both combustion is established and said furnace condition is proper where- -by if either combustion fails or said condition is improper'the heating element is energized to cause opening of said safety switch after a time period to thereby stop said fuel feeding means.

CHARLES B. SWEA'I'I'. 

